Abstract:

 1.  Having analyzed the external morphology of the genus Microula, the author

has proposed a series of criteria as bases for the construction of a classification scheme

of this genus.  The most important ones are as follows:

     1)  The normally developed stem is primitive, and the strongly abbreviated stem

more advanced.

     2)  The small inconspicuous bracts are more primitive than the large suborbicular

densely arranged ones, which almost entirely cover the flowers and the fruits.

     3)  Nutlets with small dorsal pit  are more primitive than those with larger pit

on one hand or those without it on the other.

     4)  The dorsal pit with simple margin precedes that with double margins.

     5)  Nutlets with subbasal areola precede those with lateral or apical areola.

     6)  Nutlets without glochids precede those with glochids.

     2.  Basing upon these criteria the genus Microula may be divided into six sections.

The section Schistocaryum may be the primitive one, and the others may be evolved

from it respectively.  The possible affinities between them are demonstrated in figure

no. two.

     3.  The genus Microula, containing 30 species,  is  mainly  distributed  in  the

Chinghai-Tibetan plateau and the majority of its species concentrates in the eastern

border of the plateau, and of the 30 species 26—that is 90 percent—are endemic

to China, and the remaining 4 are distributed elsewhere in China, too, and extending

southward and westward to Bhutan, Sikkim, Nepal and Kashmir respectively.  In the

region between Heishui, Province Szechuan, and Chinghai Lake there are 9 species,

which, curiously, represent all the six sections of Microula, hence this region seems to

be the center of maximum variation of this genus.  M. ovalifolia whose nutlets have

small dorsal pit and subbasal areola may be considered the most primitive species.

Thus the author is of the opinion that the western part of province Szechuan, to

which M. ovalifolia is endemic, may probably be the center of origin of the genus

Microula.